Raul,

if you have received your Green Card today, you automatically became a US citizen by act of law, the Child Citizenship Act of 2000, if either your mom or your dad is a US citizen. If that's the case, your US citizen parent and you will go to the nearest passport office and apply for a passport book and -- for $30 extra -- a passport card for you. I suggest that you apply for both, because if something happens to one of them, you'll have another proof of US citizenship.

Your parent will show ID and proof of US citizenship, and you will surrender this new Green Card and your birth certificate, showing that your parent is indeed your parent. In most cases you will get that Green Card back a few days after you received your passport(s), but it's for sentimental value only.

You can't get your passport stamped with an I-551 stamp if you are a US citizen, as you are not a Green Card holder any longer. And if you have NOT become a US citizen, you can't get your passport stamped because the Green Card is now the document showing your status as a permanent resident.